1. Field of the Invention
The present invention relates to a method of bonding or of making an adhesive bond, between two parts and, more particularly, to an improved method of bonding of two parts with each other by means of a slower hardening adhesive layer after an adjustment or positioning of the parts has been performed.
2. Prior Art
Adhesive bonding or gluing is used in many areas of engineering, for example, in electronics, electrooptics or micro-optics. Frequently it is necessary to align the parts with high precision in order to obtain a sufficiently high light transmission during coupling between the parts to be bonded together in an optical application or to guarantee reliable electrical contacting in the case of very small electrical contacts in an electronic application. According to the state of the art a number of glues or adhesives are used in this type of adhesive bond. Epoxy-based adhesives provide a particularly high bonding strength. These adhesives can be made electrically conducting by mixing a metallic filling material into them in order to permit a permanent electrical contact. Good heat conduction can be obtained with a ceramic admixture. Hardening for an extended time period at comparatively high temperature is required in order to provide a good bond with these epoxy-based adhesives or glues. A hardening temperature of up to 120.degree. C. for a time period of up to 24 hours is required in order to obtain a satisfactory adhesive force or bonding force. The higher the hardening temperature, the better the adherence. In applications which have stringent or narrow position tolerances, for example in the above-mentioned engineering fields, the relative position of the parts must not be changed during the hardening time after they have been put in the correct positions; in other words, a de-adjustment during hardening must be avoided. Thus the hardening must take place in the adjusting device, which is used for the position alignment or adjustment. This positioning apparatus for the parts is then blocked during the hardening time. In order to obtain a high production throughput either many positioning and gluing devices must be in operation simultaneously which is costly and/or the hardening time must be shortened using a high hardening temperature. However in many applications the hardening temperature is limited by the installation or operation temperature range of the parts to be glued together.
According to the state of the art in order to avoid the above-described disadvantages for a production process for larger numbers of parts, adhesives or glues are used which are transparent and hardened by ultraviolet radiation. These so-called UV adhesives are irradiated with UV light for a few seconds up to a maximum of 10 minutes. They have a comparatively short hardening time in comparison to epoxy-based adhesives. However the entire volume of the UV adhesive must be irradiated with the UV light in order to obtain a complete hardening of the adhesive. Thus at least one of the parts to be bonded must be transparent to UV light in order to obtain an adherent gluing of the two parts. Otherwise only one glue seam or bond in a freely accessible edge region of the parts to be bonded is possible. Thus the range of applications for this method of UV bonding is considerably narrowed or limited. The substantially weaker adherence of the UV bonding compound and its lower glass transition temperature, which limits the temperature operation range, are additional disadvantages for the UV bonding method.